There exist more and more sectors of economic activity that make use of ever more complex printed circuits in their products. The complication of these products has led to multilayer printed circuits becoming widespread. Such multilayer circuits are made up of a plurality of individual printed circuit plates which are subsequently fixed to one another, and electrical connections are also made between the various layers in order to obtain a complete multilayer printed circuit.
Because, since it is clearly necessary to stack the individual printed circuits with great accuracy in order to make up the final circuit, a need has arisen for implementing position-marking means on the individual inside printed circuit layers. This marking is usually formed by means of holes drilled through the insulating backing of the printed circuit at locations that are accurately defined relative to the plate and/or to the printed circuit formed thereon.
These positioning holes can be made in the insulating backing either before the conductor tracks are made, or else after they have been made. The act of drilling positioning holes runs the risk of giving rise to a certain amount of pollution because of the presence of dust on the surface of the insulating backing. This pollution naturally gives rise to poor quality deposition of conductors on the insulating backing. Thus trend is to make the positioning holes after the conductors have been made on the insulating backing.
Whichever of the two possible techniques is used, making the positioning holes by means of a machine requires the plate to be positioned initially relative to the structure of the machine, and then the punch tools to be positioned relative to said structure, so as to make the holes in the appropriate places.
The punching machines that are most frequently encountered at present require manual operations to be performed to position the punch tools relative to the printed circuit after the printed circuit has been positioned relative to the structure. When it is necessary to perform a large number of punching operations with different punching characteristics, such manual positioning is, naturally, very expensive.
That is why machines have been proposed in which the positioning of the punch tools is under program control. Nevertheless, in such machines, the operations that need to be performed to go from punching one type of printed circuit card to another type remain considerable and thus give rise to considerable losses of time, in spite of the pseudo-automatic way in which the punches are positioned. In particular, it is important to emphasize that even if positioning holes are, a priori, always of the same size, the punch tools, which are essentially constituted by a punch and a die, need to be adapted to the characteristics of the insulating backing of the printed circuit. In particular, the characteristics of the die and of the punch depend on the nature of the material constituting the insulating backing of the printed circuit and on the thickness of said insulating backing. It should be added that these manual operations of changing punches and dies give rise not only to a loss of time because of the operations themselves, but also require very accurate initial repositioning of the punch tools after a punch and die have been changed.